The present description relates to an electric machine, more particularly to a switched reluctance motor and method of using it to generate torque and electricity.
A switched reluctance motor is known and presented, for example in Japanese Patent Application Publication 2001-25286, which generates torque on its rotor by sequentially carrying electricity on coils of a plurality of salient poles of a stator by means of switching elements. The electricity sequentially carried on the stator coils generates sequentially a magnetic field on each of the stator salient poles. The magnetic field pulls a salient pole of the rotor to each of the stator salient poles, consequently generating torque.
In an automotive application, such as an electric vehicle and hybrid electric vehicle, the switched reluctance motor may be used to generate electricity. When the rotor rotates, electricity is carried on a stator coil at one of the stator salient poles that is selected as a magnetic field coil, thereby generating magnetic field on the selected stator salient pole. Alternating magnetic flux is induced and passes through the selected stator salient pole, two of the rotor salient poles and one of the unselected stator salient poles. The induced alternating magnetic flux generates electricity on another stator coil (electric generation coil) on that one of the unselected stator salient poles.
However, in this method, the induced magnetic flux is shaped in a plane perpendicular to the rotational shaft. Consequently, the distance between the magnetic field coil and the electric generation coil on the stator changes as the rotor rotates. As a result, the amplitude of generated electricity is altered, thereby causing noise in the generated electricity. This may decrease efficiency of electric generation.
The inventors herein have recognized the above disadvantages of the prior art and the need to improve the electric generation efficiency on the switched reluctance motor.